Ftp – Mount FTP folder on Synology (not CIFS)

When you receive the 'No logon servers available' it means that your DC controlling Active Directory cannot be found. Make sure that your DC is visible on the Network and that you reboot both the DC and the Synology box. The DC needs to be rebooted before the Synology reboots, otherwise it won't refresh on the network to see the change that appears.

If this fails, check your physical connections and obviously issue a ping and see if it gets to it. If that fails, check the security across the shares and also check the credentials you are using to access the shares.

The problem you do when you restart your DCs is you are not permitting the refresh to occur and thus the backup won't see it until it is last in the restart chain, so to speak. Usually you wouldn't reboot the DC unless absolutely necessary.

Yes, DFS Replication (DFSR) will be your best way of synchronising folders between the two sites, however you will need to put some work and reading in or hire a consultant.

EDIT - Don't start there, start here: http://technet.microsoft.com/en-us/library/cc782417%28v=ws.10%29.aspx

Start here: http://technet.microsoft.com/en-gb/library/cc732863%28v=ws.10%29.aspx

That guide is for 2008, but the principles are broadly the same for 2003/08/12. (Incidentally, with Windows 2003 going out of support in less than a year I think you'd be mad to put effort into shuffling the servers about and reconfiguring the environment at this point.)

One of the very first things you'll need to do is grasp the fact that DFS Replication (DFSR) and DFS Namespaces (DFSN) are two completely different features, and can be utilised independently. You could, for example, use DFSR to replicate your folders, and have the clients at each site point direct to the share on the local server, without using DFSN.

If you are using domain-based DFS Namespaces, then you will point your clients to \\domain.local\Share and when the client accesses the share they will receive a 'referral' from a DC, which will point them towards server(s) that hosts a copy of the share. In order to get the client to go to the local or 'in-site' server, the referrals are costed based on the site of the clients and servers and the cost of the site links (Active Directory Sites).

It's not dark magic, but the actual requirements and mechanisms for fulfilling them are inherently complicated. There's plenty of documentation out there, so you'll just have to do a load of googling and set up a test environment, there's no easy way around that.